ESTOP PB OPERATION 2

[JERSEYDUDE]

Is there an code issues prohibiting the reversing operation of the emergency stop switch. In other words, using the pull of the switch to stop the machine and a push to run?

 

[BrianPetersen]

I know that the Canadian standards prohibit what you propose to do, and I'm pretty sure the European standards also prohibit it. Also, resetting an emergency-stop must not cause the machine to start - that has to require a separate and deliberate action, i.e. pressing a separate "start" button tied to a latching contactor (or safety relay, or safety PLC logic bit).

What's the motivation for wanting to do it in the reversed manner?

 

[JERSEYDUDE]

Thx BP,this is a USA machine and facility. Basically this was a customer request to have the estop sw oper backwards. supposedly they are afraid of someone accidentally bumping into it and shutting the machine down even though there is a collar to prevent it. As far as the restart, yes there is a separate start button to run the machine. I am concerned over what someone does during a panic situation where seconds could count and they punch the button,then relaize you need to pull it to stop.

 

[MadMango]

You could always change from a pushbutton to a pull-cord switch, that will prevent accidental operation while still making the estop accessible. You just can't panel mount them.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[BrianPetersen]

What you're describing cannot be done in compliance with the codes that I'm familiar with. If the concern is that someone will bump the E-stop by walking past it, mount the E-stop box with the button facing up. Shielding the button to make it more difficult to press is also on shaky compliance grounds. I wouldn't risk a code violation just because the end user "wants" it. In fact, in this situation, I'd build the machine in a compliant manner and document that it's compliant (take pictures and videos) - make sure that whatever the end user does with the machine afterward can't come back to haunt you.

 

[dbaird]

NFPA 79 Electrical Standard for Industrial Machinery clearly states

shall effect an emergency stop when depressed

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[JLSeagull]

NFPA 79 - what year?
From NFPA 79 2002 (yes it could be out of date)
10.7.2 Types.
10.7.2.1 The types of devices for emergency stop shall include, but are not limited to, the following:
(1) Pushbutton-operated switches in accordance with 10.7.4
(2) Pull-cord-operated switches
(3) Foot-operated switches without a mechanical guard
(4) Push-bar-operated switches
(5) Rod-operated switches
10.7.2.2* Pushbutton-type devices for emergency stop shall be of the self-latching type and shall have positive (direct) opening operation.
10.7.2.3 Emergency stop switches shall not be flat switches or graphic representations based on software applications.

 

[BrianPetersen]

You can use those other devices as an emergency-stop, but if you use a button, it has to be in accordance with the clauses that apply to using a button - one of which is that it has to cause a stop when depressed.

Other standards may dictate whether you use a button, pullcord, etc. I know that here, you can use any of the other devices you would like and as many of them as you would like ... but there has to be an E-stop button - a "button", not a pull cord, not a push bar, not anything else - adjacent to any place where you can start the machine.